fix: MCP client SSE transport — add correct Accept headers and SSE response parsing

FastMCP 2.0 streamable HTTP requires Accept: application/json, text/event-stream
and can return text/event-stream responses with data: {...} SSE lines.

app/mcp_client.py

@@ -1,7 +1,14 @@
-"""MCP proxy client — calls DevOpsMCP's worklog/standup tools over HTTP MCP protocol."""
+"""MCP proxy client — calls DevOpsMCP's worklog/standup tools over HTTP MCP protocol.
+
+FastMCP 2.0 uses streamable HTTP transport (MCP spec §6.3.3):
+- POST to /mcp with Accept: application/json, text/event-stream
+- Server may respond with JSON or SSE stream (text/event-stream)
+- SSE responses have `data: {...}` lines containing JSON-RPC messages
+"""
 
 from __future__ import annotations
 
+import json
 import os
 from typing import Any, Dict, Optional
 
@@ -10,25 +17,36 @@ import httpx
 MCP_URL = os.environ.get("DEVOPS_MCP_URL", "http://localhost:8000")
 _MCP_ENDPOINT = f"{MCP_URL}/mcp"
 
-
-async def _call_tool(tool_name: str, arguments: Dict[str, Any]) -> Dict[str, Any]:
-    """Call a DevOpsMCP tool via MCP JSON-RPC 2.0 over HTTP."""
-    payload = {
-        "jsonrpc": "2.0",
-        "method": "tools/call",
-        "params": {"name": tool_name, "arguments": arguments},
-        "id": 1,
+_HEADERS = {
+    "Content-Type": "application/json",
+    "Accept": "application/json, text/event-stream",
 }
-    async with httpx.AsyncClient(timeout=30.0) as client:
-        resp = await client.post(_MCP_ENDPOINT, json=payload)
-        resp.raise_for_status()
-        data = resp.json()
+
+
+def _parse_sse_data(text: str) -> Dict[str, Any]:
+    """Extract JSON-RPC result from SSE stream data lines."""
+    for line in text.splitlines():
+        line = line.strip()
+        if line.startswith("data:"):
+            chunk = line[5:].strip()
+            if not chunk or chunk == "[DONE]":
+                continue
+            try:
+                msg = json.loads(chunk)
+                if "result" in msg or "error" in msg:
+                    return msg
+            except json.JSONDecodeError:
+                continue
+    return {}
+
+
+def _extract_result(data: Dict[str, Any]) -> Dict[str, Any]:
+    """Extract tool result content from JSON-RPC response."""
     if "error" in data:
         raise RuntimeError(f"MCP error: {data['error']}")
     result = data.get("result", {})
     content = result.get("content", [])
     if content and isinstance(content[0], dict):
-            import json
         text = content[0].get("text", "{}")
         try:
             return json.loads(text)
@@ -37,6 +55,27 @@ async def _call_tool(tool_name: str, arguments: Dict[str, Any]) -> Dict[str, Any
     return result
 
 
+async def _call_tool(tool_name: str, arguments: Dict[str, Any]) -> Dict[str, Any]:
+    """Call a DevOpsMCP tool via MCP JSON-RPC 2.0 streamable HTTP transport."""
+    payload = {
+        "jsonrpc": "2.0",
+        "method": "tools/call",
+        "params": {"name": tool_name, "arguments": arguments},
+        "id": 1,
+    }
+    async with httpx.AsyncClient(timeout=60.0) as client:
+        resp = await client.post(_MCP_ENDPOINT, json=payload, headers=_HEADERS)
+        resp.raise_for_status()
+
+        content_type = resp.headers.get("content-type", "")
+        if "text/event-stream" in content_type:
+            data = _parse_sse_data(resp.text)
+        else:
+            data = resp.json()
+
+        return _extract_result(data)
+
+
 async def get_worklog(
     context: str = "egmont",
     days: int = 7,